U.S. patent number 5,913,100 [Application Number 08/663,251] was granted by the patent office on 1999-06-15 for mo-w material for formation of wiring, mo-w target and method for production thereof, and mo-w wiring thin film.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Yoshiharu Fukasawa, Mitsushi Ikeda, Yasuo Kohsaka, Toshihiro Maki, Michio Sato, Yoshiko Tsuji.
United States Patent |
5,913,100 |
Kohsaka , et al. |
June 15, 1999 |
Mo-W material for formation of wiring, Mo-W target and method for
production thereof, and Mo-W wiring thin film
Abstract
A Mo-W material for the formation of wirings is discloses which,
as viewed integrally, comprises 20 to 95% of tungsten and the
balance of molybdenum and inevitable impurities by atomic
percentage. The Mo-W material for wirings is a product obtained by
compounding and integrating a Mo material and a W material as by
the powder metallurgy technique or the smelting technique or a
product obtained by arranging these materials in amounts calculated
to account for the percentage composition mentioned above. The Mo-W
material containing W in a proportion in the range of from 20 to
95% manifests low resistance and, at the same time, excels in
workability and tolerance for etchants. The wiring thin film which
is formed of the Mo-W alloy of this percentage composition is used
as address wirings and others for liquid crystal display devices.
The Mo-W target for the formation of wirings is composed of 20 to
95% of tungsten and the balance of molybdenum and inevitable
impurities by atomic percentage and allows the Mo-W wiring thin
film to be produced with high repeatability.
Inventors: |
Kohsaka; Yasuo (Yokohama,
JP), Fukasawa; Yoshiharu (Yokohama, JP),
Tsuji; Yoshiko (Kawasaki, JP), Ikeda; Mitsushi
(Yokohama, JP), Sato; Michio (Yokohama,
JP), Maki; Toshihiro (Yokohama, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
|
Family
ID: |
18035262 |
Appl.
No.: |
08/663,251 |
Filed: |
September 6, 1996 |
PCT
Filed: |
December 14, 1994 |
PCT No.: |
PCT/JP94/02095 |
371
Date: |
September 06, 1996 |
102(e)
Date: |
September 06, 1996 |
PCT
Pub. No.: |
WO95/16797 |
PCT
Pub. Date: |
June 22, 1995 |
Foreign Application Priority Data
|
|
|
|
|
Dec 14, 1993 [JP] |
|
|
5-312936 |
|
Current U.S.
Class: |
428/546; 428/385;
257/E21.011; 257/E21.582; 257/E23.163 |
Current CPC
Class: |
H01L
21/76838 (20130101); H01L 23/53257 (20130101); H01L
28/60 (20130101); G02F 1/136286 (20130101); C23C
14/3414 (20130101); B22F 1/0003 (20130101); C22C
27/04 (20130101); Y10T 428/12014 (20150115); Y10T
428/12826 (20150115); H01L 2924/0002 (20130101); Y10T
428/1284 (20150115); G02F 1/136295 (20210101); Y10T
428/2951 (20150115); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
B22F
1/00 (20060101); C22C 27/00 (20060101); C22C
27/04 (20060101); C23C 14/34 (20060101); H01L
23/532 (20060101); H01L 21/70 (20060101); G02F
1/1362 (20060101); H01L 21/02 (20060101); G02F
1/13 (20060101); H01L 21/768 (20060101); H01L
23/52 (20060101); C22C 027/04 (); C23C 014/34 ();
B22F 003/00 () |
Field of
Search: |
;428/385,428
;313/60 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3778654 |
December 1973 |
Hueschen et al. |
|
Foreign Patent Documents
|
|
|
|
|
|
|
58-7864 |
|
Jan 1983 |
|
JP |
|
60-11479 |
|
Mar 1985 |
|
JP |
|
3-9177 |
|
Feb 1991 |
|
JP |
|
3-130360 |
|
Jun 1991 |
|
JP |
|
3-150356 |
|
Jun 1991 |
|
JP |
|
5-194064 |
|
Aug 1993 |
|
JP |
|
PCT/JP 94/02095 |
|
Dec 1994 |
|
WO |
|
Primary Examiner: Scheiner; Laurie
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Claims
We claim:
1. A Mo-W target for the formation of wirings, comprising a
material consisting essentially of 20 to 95% by atomic percentage
of tungsten and the balance of molybdenum and inevitable impurities
and possessing a relative density of not less than 98%, an average
particle diameter of crystal grains of not more than 200 .mu.m, and
a Vickers hardness, Hv, of not more than 350.
2. The Mo-W target according to claim 1, wherein said tungsten and
said molybdenum are alloyed.
3. The Mo-W target according to claim 1, wherein the material
comprises a sintered composite obtained by a powder metallurgy
technique.
4. The Mo-W target according to claim 1, wherein the material
comprises a material obtained by hot working a sintered composite
produced by the powder metallurgy technique.
5. The Mo-W target according to claim 1, wherein the material
comprises an alloy ingot produced by a smelting technique.
6. The Mo-W target according to claim 1, wherein the material
comprises a uniform solid solution phase Mo and W.
7. A method for producing a Mo-W target for the formation of
wiring, comprising:
shaping a mixed powder composed of 20 to 95% atomic percent of
tungsten and the balance of molybdenum and inevitable impurities
into a shaped mass;
sintering the shaped mass in a reducing atmosphere;
hot working the sintered mass to form a target having a relative
density of less than 98%; and
subjecting the target obtained in said hot working step to a
strain-relieving heat treatment so that the target possesses an
average particle diameter of crystal grains of not more than 200
.mu.m, and a Vickers hardness, Hv, of not more than 350.
8. The method according to claim 7, which further comprises a step
of subjecting the worked material obtained in said hot working step
to a strain relieving heat treatment.
Description
DESCRIPTION
1. Technical Field
This invention relates to a Mo-W material for the formation of
wiring, a Mo-W target for the formation of wiring and a method for
the production thereof, and a Mo-W wiring thin film.
2. Background of Art
In recent years, the active matrix type liquid crystal display
devices using as a switching element thereof a thin film transistor
(hereinafter referred to as "TFT") formed by using an amorphous
silicon (hereinafter referred to as "a-Si") film have been
attracting attention. This is because there exists the possibility
that a panel display having a large area, high accuracy, and high
quality, namely a flat television, will be realized inexpensively
by forming a TFT array with an a-Si film producible at low
temperature on an inexpensive glass substrate.
In the construction of a display of a large area, however, the
amount of resistance offered by the address wiring to be laid
therein is increased because the gross length of the address wiring
is inevitably increased to a marked extent. This increase in the
amount of resistance of the address wiring entrains the problem of
conspicuously delaying gate pulses to be given to switch elements
and rendering control of a liquid crystal difficult. It is,
therefore, necessary that the delay of gate pulses be avoided while
retaining at least such parameters as wiring widths intact.
As one measure to avoid the delay of gate pulses, the idea of
forming the address wirings with a wiring material which possesses
as low resistivity as permissible may be conceived. At present, the
Mo-Ta alloy film is often used as the material for the address
wirings. Since this alloy film has such large resistivity as about
40 .OMEGA..multidot.cm, it is held that the resistivity of the
Mo-Ta alloy film renders difficult the realization of a display of
a large area. Particularly, the direct-view type display of high
accuracy using about 1000 address wirings is considered to require
a wiring material possessing resistivity of not more than about 20
.mu..OMEGA.cm.
The new wiring material of such quality as mentioned above is
required to possess such characteristics as will be shown below in
addition to the low resistivity mentioned above. Since the
insulation between the wirings and the address wirings which are
formed on an interlayer insulating film must be heightened by
improving the step coverage of the interlayer insulating film
formed on the address wirings, this new wiring material must be
capable of being tapered.
The realization of a liquid crystal display device which, owing to
the formation of address wirings with a wiring material of low
resistance, is enabled to repress the delay of gate pulses and, at
the same time, acquire necessary insulation and enjoy high
reliability is yearned for. The desire of this kind has been
expressed not merely for liquid crystal display devices having a
display of a large area but equally for liquid crystal display
devices having wirings and wiring intervals narrowed for the
purpose of exalting the accuracy of display or liquid crystal
display devices having an opening ratio improved by decreasing the
width of wirings.
The conventional liquid crystal display devices have such problems
as shown below in addition to those already remarked above. FIG. 5
is a cross section of a TFT (switching element) and a storage
capacity part to be used in a liquid crystal display device.
By sputtering a Mo-Ta alloy, a gate electrode 2, address wirings,
address wirings, and a Cs line 9 are simultaneously formed on a
glass substrate 1 as shown in FIG. 5. Through the medium of a gate
insulating film 3 which is formed thereon, an a-Si active layer 4
is superposed. On the opposite end parts of this active layer 4,
n.sup.+ a-Si layers 5a and 5b are deposited. Then, through the
medium of the gate insulating film 3, an ITO picture element
electrode 8 is formed. Subsequently, an Al source electrode 6a
having a part thereof connected to the n.sup.+ a-Si layer 5a, a
drain electrode 6b having a part thereof connected to the n.sup.+
a-Si layer 5b and the picture element electrode 8, and data wirings
are simultaneously formed.
The conventional TFT shown in FIG. 4 has a picture element
electrode and data wirings formed in one and the same layer without
intervention by an insulating film and, therefore, has the
possibility of forming a short circuit and giving birth to point
defects. To avoid the point defects, the configuration which has a
source electrode, a drain electrode, and data wirings laid out
first, an interlayer insulating film subsequently formed thereon,
and a picture element electrode finally superposed thereon has been
conceived and studied as a possible measure of improvement. To
realize this configuration, the following requirements must be
satisfied.
(1) The data wirings and others should possess excellent tolerance
for the etchant for use on the interlayer insulating film and to
the ITO etchant for the picture element electrode.
(2) For the purpose of improving the step coverage of the
interlayer insulating film thereby heightening the insulation
between the data wirings and the picture element electrode, the
data wirings should be capable of being tapered.
Since none of the wiring materials developed to date fulfils the
requirements mentioned above, it has been difficult to realize the
configuration mentioned above and improve the reliability of a
liquid crystal display device. Since it is important to lower the
ratio of occurrence of point defects for the development of a
display of a large area, the desirability of developing a liquid
crystal display device of such high reliability has been finding
growing recognition. For this reason, it is essential to develop a
wiring material which satisfies the requirements mentioned above
and also a target for the formation of a wiring.
Incidentally, the Al and the Ta type alloy form an oxide film on
their surfaces and offer an increased contact resistance to the
metallic wirings which are formed in the layer superposed thereon
and, therefore, require a step for the removal of the oxide film
from their surfaces. They further require a barrier metal to
prevent ITO and Al from reacting with each other and, therefore,
are at a disadvantage in inevitably increasing the number of steps
of the process of manufacture.
An object of this invention is to provide a material for wirings
having low resistance and permitting the work of tapering, a target
for the formation of wiring, and a wiring thin film. A further
object of this invention is to provide a material for wirings
having low resistance and possessing high tolerance for the
etchants for an interlayer insulating film, ITO, or the like, a
target for the formation of wirings, and a wiring thin film.
Another object of this invention is to provide a method for the
production of a target for the formation of wirings, which method
permits such a target for the formation of wirings as mentioned
above to be manufactured with high repeatability.
DISCLOSURE OF THE INVENTION
The present inventors, with a view to attaining the objects
mentioned above, have systematically continued experiments and
studies on various metals and alloys in search for a wiring
material fit for display devices such as liquid crystal display
devices to find for the first time in the art that the film of an
alloy composed of molybdenum (Mo) and tungsten (W) at a ratio in a
specific range has low resistivity and highly satisfactory
formability as compared with the film made solely of either of the
component elements, Mo and W. This invention has been perfected as
a result.
The first aspect of this invention, i.e. the Mo-W material for the
formation of wirings, is characterized by the fact that the
material as viewed integrally is composed of 20 to 95% of tungsten
and the balance of molybdenum and inevitable impurities by atomic
percentage.
The second aspect of this invention, i.e. the Mo-W target for the
formation of wiring, is characterized by the fact that the target
as viewed integrally is composed of 20 to 95% of tungsten and the
balance of molybdenum and inevitable impurities by atomic
percentage. The Mo-W target of this invention for the formation of
wiring is characterized by particularly consisting essentially of a
Mo-W alloy composed of 20 to 95% of tungsten and the balance of
molybdenum and inevitable impurities by atomic percentage and the
Mo-W alloy having relative density of not less than 99%, average
grain size of not more than 200 .mu.m, and Vickers hardness, Hv, of
not more than 350.
The third aspect of this invention, i.e. the Mo-W wiring thin film,
is characterized by being composed of 20 to 95% of tungsten and the
balance of molybdenum and inevitable impurities by atomic
percentage.
The method of this invention for the production of a Mo-W target
for the formation of wirings is characterized by comprising a step
of shaping a mixed powder composed of 20 to 95% of tungsten and the
balance of molybdenum and inevitable impurities by atomic
percentage, a step of sintering the shaped mass obtained in the
shaping step in an inert ambience, and a step of hot working the
sintered mass obtained in the sintering step.
Now, this invention will be described more specifically below.
The Mo-W material of this invention for the formation of wirings is
so prepared as to be composed, as viewed integrally, of 20 to 95%
of tungsten and the balance of molybdenum and inevitable impurities
by atomic percentage. As concrete forms of the Mo-W material of
this invention for the formation of wirings, the following
materials may be cited, for example.
(A) The materials obtained by compounding and integrating
(alloying, for example) a Mo material and a W material in such a
mixing ratio as to account for a proportion of W in the range of
from 20 to 95% by atomic percentage; such as, for example, sinters
produced by the powder metallurgy technique and ingots by the
smelting technique.
(B) The materials obtained by combining a Mo material and a W
material so that the proportion of W, as viewed integrally, may be
in the range of from 20 to 95% by atomic percentage.
If the proportion of W in the Mo-W material mentioned above is less
than 20% by atomic percentage, the Mo-W material will suffer undue
increase in resistance and undue decrease in the tolerance for such
etchants as used on the interlayer insulating film and the ITO.
Conversely, if this proportion of W exceeds 95%, the Mo-W material
will likewise suffer undue increase in resistance. In other words,
when the Mo-W material has a proportion of W in the range of from
20 to 95%, it possesses low resistance and excels in tolerance for
etchants. Further, the Mo-W material which has the percentage
composition mentioned above has the advantage that, when formed in
the shape of a thin film, it permits a tapering work.
Preferably, the proportion of w in the Mo-W material of this
invention for the formation of wirings is in the range of from 20
to 70% by atomic percentage. So long as the proportion of W falls
in this range, the wiring thin film which is formed of the Mo-W
material by the sputtering technique, for example, is obtained at a
practically excellent sputter rate. For the sake of allowing the
Mo-W material to acquire superior tolerance for etchants as well as
such an excellent sputter rate as mentioned above, the proportion
of W ought to be in the range of from 25 to 45%.
In order for the wirings produced with the Mo-W material of this
invention for the formation of wiring to acquire improved
characteristic properties, the content of the impurity elements in
the Mo-W material ought to be decreased to the fullest possible
extent (which remarks hold good for the Mo-W target and the Mo-W
wiring thin film). The content of oxygen as an impurity, for
example, ought to be not more than 500 ppm, preferably not more
than 200 ppm, more preferably not more than 100 ppm, and still more
preferably not more than 50 ppm. The reason for this restriction of
the oxygen content is that the Mo-W material generally suffers
occurrence of numerous pores and degradation of density when the
oxygen content is unduly large. The degradation of density results
in aggravating the occurrence of particles. To lower the oxygen
content, such measures as subjecting the powder to reduction with
hydrogen or improving the sintering property may be adopted.
The Mo-W wiring thin film of this invention is made of a Mo-W alloy
of the percentage composition mentioned above. The reason for
specifying the proportion of W in the composition and the preferred
range of this proportion which exist in this case are the same as
described above. The address wirings as in the liquid crystal
display device which are made of the Mo-W wiring thin film operate
as components of low resistance to the gate pulses. The gate pulses
which are transmitted through the address wirings, therefore, are
hardly affected by the delay action which originates in the
resistant components of the address wirings. Consequently, to the
switching elements which are serving to drive liquid crystals, gate
pulses which have no delay are delivered.
Further, since the Mo-W wiring thin film of this invention is
capable of being tapered, the interlayer insulating film which is
formed on the address wiring made of the wiring thin film enjoys a
highly satisfactory step coverage. As a result, high dielectric
strength is obtained between the wirings and the address wirings to
be formed on the interlayer insulating film. The Mo-W wiring thin
film of this invention possesses excellent tolerance for such
etchants as are used on the interlayer insulating film, the ITO, or
the like. It is, therefore, capable of exalting the insulation
between the data wirings and picture element electrodes. Owing to
these features, liquid crystal display devices of high reliability
can be realized even when they are produced with display regions of
a large area.
The Mo-W wiring thin film of this invention effectively operates
not only in liquid crystal display devices aimed at enlarging areas
of display but also in liquid crystal display devices having
wirings and intervals of wirings narrowed by exalting the accuracy
of display or liquid crystal display devices having opening ratios
improved by decreasing widths of wirings. The Mo-W wiring thin film
of this invention ideally realizes the reduction of widths of
wirings and intervals of wirings. Further, the Mo-W wiring thin
film of this invention is effectively used not only as wirings or
others for liquid crystal display devices but also as wirings as
for plasma display devices, solid display devices, and flat display
devices using a field-emission type cold cathode.
The Mo-W wiring thin film of this invention is further at an
advantage in the fact that an oxide film formed on the surface
thereof has only small resistance. For this reason, it is allowed
to form ideal contact as with metallic wirings laid in an overlying
layer without requiring a preparatory treatment to remove the oxide
film. Unlike the conventional liquid crystal display devices,
therefore, the liquid crystal display devices which are produced by
the use of the Mo-W wiring thin film of this invention can be
constructed with the gate electrodes, the address wirings, and the
Cs wires thereof in a state having their surfaces coated with an
oxide film.
The Mo-W target of this invention for the formation of wirings
allows the Mo-W wiring thin film possessing such characteristic
properties as mentioned above to be formed with high repeatability
by such a thin film forming method as the sputtering technique. It
utilizes the Mo-W material of this invention for the formation of
wirings. The Mo-W target for the formation of wirings is so
prepared as to be composed, as viewed integrally, of 20 to 95% of
tungsten and the balance of molybdenum and inevitable impurities by
atomic percentage for the same reason as given above with respect
to the Mo-W material for the formation of wirings. The reason for
specifying the proportion of W in the composition and the preferred
range of this proportion are the same as already described
above.
The composition of the Mo-W wiring thin film can not be generally
fixed because it is widely varied by such numerous conditions
existing during the formation of the wiring thin film as, for
example, the ambience in which the sputtering is carried out and
the magnitude of the voltage used therefor. The Mo-W wiring thin
film of fully satisfactory quality can be obtained so long as the
proportion of W falls in the range mentioned above.
The Mo-W target of this invention for the formation of wirings is
allowed to assume a varying form. As concrete forms of the Mo-W
target, the same materials as cited above as concrete forms of the
Mo-W material [the materials of (A) and (B)] may be cited. Since Mo
and W are different in sputter efficiency, a target such as, for
example, an alloy target which is produced by compounding and
integration a Mo material and a W material in the form of (A)
mentioned above proves particularly suitable for the purpose of
diminishing the difference of composition between the target and
the wiring thin film to be obtained and attaining a uniform film
composition.
The Mo-W alloy target mentioned above is obtained with a varying
density and texture, depending on the method of production and the
conditions of production such as, for example, particle diameters
of powders, forming conditions, sintering conditions, and
mechanical working conditions to be involved in the powder
metallurgy technique which will be described more specifically
hereinbelow and smelting and casting conditions to be involved in
the smelting technique. The density, texture, and others of the
target have their effects exerted on the properties of the wiring
thin film to be ultimately produced. For the purpose of precluding
the occurrence of particles during the work of sputtering and
improving the properties of the Mo-W wiring thin film, therefore,
the Mo-W target ought to possess a dense and fine metallic texture.
The particles form a cause for producing breaks or short circuits
in the wiring. To be more specific, the relative density of the
Mo-W target ought to be not less than 98% and the average diameter
of crystals thereof to be not more than 200 .mu.m.
Since the Mo-W target mentioned above is a polycrystal formed by
the aggregation of grains of different orientations, it has the
sputter rate thereof varied by the orientations of the grains.
Thus, the sputtered surface of the Mo-V target gains in
irregularity and widens differences of level between the grains in
proportion as the grains grow in size. The sputter grains,
therefore, are liable to adhere to and accumulate on the stepped
levels and the grain surfaces. Particularly, the sputter grains
impinging on the target in diagonal directions unstably accumulate
in the central part and the terminal parts of the target. The
sputter grains which are unstably accumulated as described above
(or a film formed by the sputter grains so accumulated) separate
and fall off during the course of sputtering and possibly form a
cause for the occurrence of particles. Further, the parts of large
differences of level are caused to generate splashes by abnormal
discharge and induce emission of particles.
The occurrence of particles mentioned above can be repressed by
decreasing the sizes of the grains in the Mo-W target. The average
diameter of the grains, therefore, ought to be not more than 200
.mu.m, preferably not more than 100 .mu.m, and more preferably not
more than 50 .mu.m. The term "diameter of grains" which is used in
this invention refers to the magnitude of "(major diameter+minor
diameter)/2" of the grains observed in a 100-magnification section
of a ground surface taken arbitrarily in the direction of the
sputter surface. The average diameter of grains means the average
of the diameters of the grains which are present within not less
than 30 fields of view selected in the polished surface mentioned
above.
When pores are present in the Mo-W target, the sputter grains which
are beaten out by the Ar ions driven into the pores during the
sputtering work are accumulated on the edges of the pores and
consequently suffered to form protuberances. These protuberances
induce abnormal discharge and give rise to particles. The
occurrence of these particles can be repressed by densifying the
Mo-W target. The relative density of the Mo-W target, therefore,
ought to be not less than 98%, preferably not less than 99%, and
more preferably 100%.
The residual machining strain in the Mo-W target also has an effect
to bear on the occurrence of particles. If the target retains large
residual machining strain, the residual strain induces the sputter
rate to be locally varied. The resultant difference in the sputter
rate produces numerous stepped parts in the sputter surface and
increases the amount of particles suffered to occur. The machining
strain can be eliminated by a heat treatment and this elimination
can be rated by the hardness which decreases in proportion as the
machining strain decreases. The Mo-W target ought to possess
Vickers hardness of not more than 400, preferably not more than
300, and more preferably not more than 250.
The Mo-W target mentioned above, depending on the method of
production thereof and the conditions for the production, can
assume a varying texture such as, for example, a texture of a
uniform solid solution phase of Mo and W, a texture having an
elemental phase of Mo and/or W in a solid solution phase of Mo and
W, and a texture having a solid solution phase of Mo and W in an
elementary phase of Mo and/or W. These textures may be selected to
suit particular properties aimed at. Particularly, since Mo and W
are expected to be uniformly distributed in the target, the Mo-W
target ought to have a texture of a uniform solid solution phase of
Mo and W.
As more concrete forms of the Mo-W target of this invention for the
formation of wirings, the following targets may be cited, for
example.
(a) The targets which are produced by the powder metallurgy
technique using a mixed powder containing a Mo powder and a W
powder at a prescribed mixing ratio.
(b) The targets which are produced by the smelting technique using
Mo and W in amounts calculated to satisfy a prescribed mixing
ratio.
(c) The targets in which target pieces formed of Mo and inevitable
impurities and target pieces formed of W and inevitable impurities
are arranged complexly as divided by kind of metal, with the mixing
ratio of Mo and W being adjusted by the ratio of areas of the two
target pieces.
The targets (a) and the targets (b) are concrete examples of the
form of (A) mentioned above. The targets (c) are concrete examples
of the form of (B) mentioned above.
One example of the method for the production of the target (a)
mentioned above will be described below. First, a uniform mixed
powder is prepared by mixing Mo powder and W powder in a ball mill.
In this case, nylon or a ceramic substance may be used as the
material for the balls. The amount of impurities suffered to be
incorporated in the target can be decreased, however, by using Mo
or W as the material for the inner wall of the ball mill or for the
balls to be used in the ball mill.
Then, the mixed powder mentioned above is packed as in a carbon
mold and sintered. For this sintering, a hot press disposed in a
vacuum can be used. For the purpose of improving the sintering
property of the mixed powder and densifying the resultant sinter,
the combination of isotropic pressure forming as by the use of a
cold hydrostatic press (CIP) with sintering carried out in such a
reducing ambience as the ambience of hydrogen may be adopted. The
sinter obtained by such a method as described above is further
subjected to a HIP treatment or to such a hot working operation as
forging or rolling to prepare effectively a more densified blank
for the target. The hot press ought to be carried out under the
conditions of heating temperature of not less than 1973 K and
planar pressure of not less than 20 MPa, preferably heating
temperature of not less than 2073 K and planar pressure of not less
than 30 MPa. The sintering which follows the pressure forming ought
to be carried out at a temperature of not less than 1973 K,
preferably not less than 2073 K. The HIP treatment is
advantageously carried out under the conditions of heating
temperature of not less than 1773 K and pressure of not less than
150 MPa, preferably heating temperature of not less than 2073 K and
pressure of not less than 180 MPa. These lower limits are essential
because the sintering will not easily proceed and the blank for a
target will not be easily obtained from a sinter of high density if
the temperature of heating and the planar pressure are unduly
low.
The blank for a target which is obtained by the powdery metallurgy
technique mentioned above is subjected to such a mechanical working
as grinding to produce a Mo-W target in a prescribed shape.
The target (b) is produced by the following method, for example.
First, a sinter composed of Mo, W, and inevitable impurities is
prepared by the powder metallurgy technique and an ingot is
produced by subjecting the sinter to the smelting technique such as
electron fusion. Then, the ingot is subjected optionally to hot
working such as forging or rolling and then to such a mechanical
working as grinding to produce a Mo-W target in a prescribed
shape.
The Mo-W target of this invention for the formation of wirings, for
the purpose of preventing the occurrence of particles during the
sputtering operation, ought to satisfy such conditions imposed
concerning density, texture, and others as described above. For
this reason, it is advantageous to adopt the method of production
which combines powder metallurgy technique with hot working. When
the sinter produced by the powder metallurgy technique is subjected
to hot working, the blank for a target which is consequently
obtained is allowed to retain a fine grain size and attain
heightened density as well. This blank allows production of a Mo-W
target having relative density of not less than 98% and an average
grain size of not more than 200 .mu.m, for example. The blank for a
target which is obtained by the smelting technique tends to suffer
coarsening of grain size and, therefore, has the possibility of
losing mechanical strength and sustaining a crack and other damage
while undergoing hot working.
The sinter which is destined to undergo the hot working mentioned
above ought to possess relative density of not less than 90%. If
the relative density of the sinter is unduly low, the hot working
which is performed thereon will possibly fail to densify ultimately
the blank for the target as expected. The sinter which is subjected
to the hot working ought to be the product of sintering a pressure
formed mass obtained as by CIP. In the case of the sinter which is
obtained by a hot press, the possibility of Mo and W reacting with
the carbon mold will arise when the temperature is raised to a
level at which necessary densification is attained.
It is safely concluded that the Mo-W target of the present
invention for the formation of wirings is produced advantageously
by a method which comprises a step of shaping (particularly by the
CIP or the like) a mixed powder prepared at a prescribed percentage
composition (W: 20.about.95 at %), a step of sintering the shaped
mass in such a reducing ambience as the ambience of hydrogen, and a
step of hot working the resultant sinter. The blank for a target
which is obtained at the end of the step of hot working, for the
purpose of being relieved of residual machining strain, ought to
undergo further a strain-relieving heat treatment.
The specific conditions under which the method for the production
of the target mentioned above is to be carried out are as follows.
For the production of the Mo-W target which possesses such density,
metal texture, and hardness as mentioned above, the temperature of
treatment during the sintering in the reducing ambience such as the
ambience of hydrogen, the temperature of treatment during the hot
working and the ratio of hot working, the temperature of the
subsequent heat treatment, or the like constitute important
factors.
First, the sintering temperature in the reducing ambience such as
the ambience of hydrogen affects the density of the blank for a
target. The sintering temperature, therefore, ought to be not less
than 2173 K. If the sintering temperature is less than 2173 K, it
will be difficult to increase the relative density of the blank
beyond 98% even when the sinter is subsequently hot rolled. Though
the density is improved in proportion as the duration of the
sintering is lengthened, the productivity of the sintering is
degraded in proportion as the duration is increased. Thus, the
sintering time is proper in the approximate range of from 5 to 30
hours. The temperature of treatment ought to not less than 2272 K,
preferably not less than 2473 K and the sintering time ought to be
in the approximate range of from 10 to 25 hours.
The temperature of the treatment of hot working constitutes an
important factor for preventing the sinter under treatment from
sustaining a crack and ensuring stable production of the blank.
Particularly since pure tungsten is liable to be suddenly
embrittled at temperatures below 1473 K, the temperature of the
treatment ought to be heightened in proportion as the W content in
the sinter under treatment is increased. Advantageously, therefore,
the temperature of the treatment is not less than 1673 K,
preferably not less than 1873 K. In consideration of the heat
equalizing property of the sinter, the heating time ought to be in
the approximate range of from 2 to 8 hours. Further, when the hot
working is implemented in the form of hot rolling, the ratio of
reduction by rolling ought to be not less than 50% for the purpose
of raising the relative density of the target beyond 98%.
Advantageously, the ratio of reduction is not less than 60%,
preferably not less than 70%. The term "ratio of reduction (%)"
which is used in this invention refers to the ratio of the
thickness of the sinter before the rolling to the thickness thereof
after the rolling and is expressed as [(thickness of the sinter
before rolling-thickness thereof after rolling)/thickness thereof
before rolling).times.100].
The strain-relieving heat treatment which is performed subsequently
to the hot rolling advantageously proceeds at temperatures in the
range of from 1473.about.1923 K. If the temperature of this heat
treatment is less than 1473 K, the possibility arises that the
relief of residual strain will not be fully attained. Conversely,
if this temperature exceeds 1923 K, the possibility arises that
pores will occur in the blank and induce generation of particles.
It is more advantageous to set the temperature of the
strain-relieving heat treatment in the range of from
1673.about.1823 K.
It is advantageous from the viewpoint of preventing the occurrence
of particles during the formation of a thin film, that the targets
(a) and the targets (b) mentioned above be produced in one-piece
masses. For the purpose of producing targets in large sizes, it is
allowable to use a plurality of targets of one and the same
composition in a suitable combination. In this case, the plurality
of targets are fixed by soldering as to a backing plate. It is
advantageous for the sake of preventing the generation of particles
particularly from the edge parts thereof that the adjoining targets
be joined by means of diffusion. For the union thereof by
diffusion, various methods are available such as, for example, a
method for directly joining the adjacent targets, a method for
joining the adjoining targets through the medium of Mo and/or W
disposed along their joints, and a method for joining the adjoining
targets through the medium of a plating layer of Mo and/or W
disposed along their joints.
Now, one example of the method for the production of a target (c)
will be described below. First, Mo target pieces and W target
pieces are produced by such a smelting technique as the powder
metallurgy technique or electron fusion. The resultant ingots are
optionally subjected to mechanical working. A Mo-W target is
obtained in a prescribed shape by dividing the ingots by kind of
metal and arranging them complexly. The compounding ratio of Mo and
W is adjusted as required by controlling the areal ratio of the two
metals involved.
The characteristic properties of the thin film to be obtained are
affected by the textures and others of the target pieces. The
particle diameters of the powders, the condition of shaping, the
condition of sintering, and the condition of mechanical working in
the powder metallurgy technique and the melting and casting
conditions in the smelting technique, therefore, ought to be
suitably selected. The targets to be produced, therefore, are
enabled to acquire widely varied textures, crystal structures, and
others by varying the various production conditions as described
above. It is advantageous that the texture, density, and others of
each target piece be in conformity with those of the alloy target
mentioned above.
The target (c) comprises a complexly arranged plurality of target
pieces. For the purpose of precluding the generation of particles
particularly from the edge parts of target pieces, it is necessary
that the adjacent target pieces be joined by diffusion. For the
union thereof by diffusion, various methods are available such as,
for example, a method for directly joining the adjacent targets, a
method for joining the adjoining targets through the medium of Mo
and/or W disposed along their joints, and a method for joining the
adjoining targets through the medium of a plating layer of Mo
and/or W disposed along their joints.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the relation between the resistivity
and the W content of a Mo-W alloy,
FIG. 2 is a diagram showing the relation between the etching rate
of a Mo-W alloy in a varying etchant and the W content of the Mo-W
alloy,
FIG. 3 is a diagram showing the relation between the stress and the
W content of a Mo-W alloy,
FIG. 4 is a diagram showing the relation between the W content and
the sputter rate in a Mo-W alloy film produced by sputtering a Mo-W
target,
FIG. 5 is a cross section of a TFT and a storage capacity part to
be used in a liquid crystal display device,
FIG. 6 is a cross section of a TFT and a storage capacity part be
used in another liquid crystal display device,
FIG. 7 is a cross section of a TFT and a storage capacity part to
be used in another liquid crystal display device,
FIG. 8 is photomicrograph showing in a magnified scale the metallic
texture of a Mo-W target formed in one working example of this
invention,
FIG. 9 is a photo-micrograph showing in a magnified scale the
metallic texture of a Mo-W target formed in another working example
of this invention,
FIG. 10 is a photomicrograph showing in a magnified scale the
metallic texture of a Mo-W target formed in yet another working
example of this invention, and
FIG. 11 is a photo-micrograph showing in a magnified scale the
metallic texture of a Mo-W target formed for referential
purpose.
MODE FOR EMBODYING THE INVENTION
Now, this invention will be described below with reference to
working examples.
EXAMPLE 1
A plurality of uniform mixed powders were obtained by weighing out
a Mo powder having an average particle diameter of 10 .mu.m and a W
powder having an average particle diameter of 10 .mu.m in amounts
calculated to account for varying atomic percentages, placing each
set of Mo and W powders in a ball mill having the inner wall coated
with Mo, and mixing them for 48 hours by the use of balls made of
nylon. The mixed powders were each packed in a carbon mold and then
sintered in a vacuum hot press at a temperature of 2073 K under
planar pressure of 30 MPa for five hours to obtain sinters having a
density of 97%. The sinters thus obtained were each subjected to
the mechanical workings of cutting and grinding to produce Mo-W
targets measuring 250 mm in diameter and 8 mm in thickness and
having a varying composition.
These Mo-W targets were each bonded with an In type solder to a
packing plate made of oxygen-free copper and then set in place in a
sputtering device. In this sputtering device, the targets were set
at a distance of 70 mm from a glass substrate destined to form a
film-forming substrate, the glass substrate was heated, and a DC
power source was turned on to sputter the targets with an input
power of 1 kW under an Argon pressure of 0.5 Pa, to form respective
Mo-W alloy films.
The Mo-V alloy films consequently obtained were tested for
resistivity. The results are shown in relation to respective W
contents in FIG. 1. It is clearly noted from FIG. 1 that the Mo-W
wiring thin films (having W contents of from 20 to 95 at %) of this
invention had notably lower magnitudes of resistivity than 40
.mu..OMEGA.cm and that these magnitudes were lower than those of
resistivity of the films formed of the component materials, Mo film
and W film, of this invention.
Now, an example of the use of a wiring thin film formed with the
Mo-W target mentioned above in a liquid crystal display device will
be described below. FIG. 5 is a cross section showing one example
of the arrangement of a TFT (switching element) and a storage
capacity part to be used in the liquid crystal display device. The
construction of the TFT and the storage capacity part and the
process thereof will be described.
On a glass substrate 1, the Mo-W target of this invention mentioned
above was sputtered in 300 nm to form simultaneously a gate
electrode (control electrode) 2, an address line, and a Cs line 9.
Then, by the plasma CVD, a-Si islands were formed by continuously
depositing an oxide film 3 in 350 nm, an a-Si active layer 4 in 300
nm, and n.sup.+ a-Si layers 5a and 5b each in 50 nm. Subsequently,
ITO was sputtered in 120 nm to form a picture element electrode 8.
The portion of SiO.sub.x in the contact part was etched with dilute
hydrofluoric acid (HF) to form a contact hole. Then, by sputtering
a prescribed wiring metal such as, for example, Al and wet etching
it, a source electrode (first electrode) 6a, a drain electrode
(second electrode) 6b, and data wiring were simultaneously formed.
In this case, the surface required an oxidizing treatment prior to
the sputtering of Al.
The Mo-W wiring thin film of this invention formed here with the
Mo-W target of this invention had low resistivity and, therefore,
the address wiring which was formed with this wiring thin film
showed proportionately low resistivity. As a result, the wiring
resistance caused no delay in the gate pulses and the relevant
switching element obtained gate pulses which were not delayed.
Since the Mo-W wiring thin film of this invention was capable of
being tapered, the interlayer insulating film deposited on the
address wirings formed with this alloy film enjoyed fully
satisfactory step coverage and allowed maintenance of high
dielectric strength. The liquid crystal display device of high
reliability could be realized even when the display region was
formed with a large area. The relation between the mixing ratio of
the Mo-W target and the taper angle is shown in Table 1.
TABLE 1 ______________________________________ Target composition
(at %) W Mo Taper angle ______________________________________ 0
100 20.degree. 30 70 25.degree. 50 50 32.degree. 70 30 37.degree.
100 0 48.degree. ______________________________________
The taper angle was determined by observing the section of a sample
thin film with the aid of SEM and measuring the angle of the thin
film with the glass substrate. It is clearly noted from Table 1
that the taper angle increased in proportion as the proportion of W
increased and that the tapering was obtained satisfactorily while
the target composition as within the range specified by this
invention.
Then, for the purpose of testing for chemical resistance, the Mo-W
alloy films of the varying compositions mentioned above were
treated with the etchant for ITO, a material for the picture
element electrode, BHF, an etchant for the interlayer insulating
film, and the etchant for Al to find respective etching rates
(nm/min). The results are shown in FIG. 2.
It is clearly noted from FIG. 2 that the etching rate of the
Mo-W-alloy film was not more than 8 nm/min with the etchant for
ITO, not more than 3 to 40 nm/min with the etchant for Al, and
perfectly nil with the BHF, the etchant for the. interlayer
insulating film. It is remarked that absolutely no etching occurred
when the proportion of W was 50 at % or over. The data indicate
that such wirings as gate electrodes and data lines which underlie
the interlayer insulating film are not corroded by any of the
etchants mentioned above even when the interlayer insulating film
is suffered to form pinholes therein. Thus, the liquid crystal
display device using the interlayer insulating film is at an
advantage in enjoying ample freedom in the design of
structure/design of process of the component layers from the
interlayer insulating film upward.
FIG. 3 shows the results of the test performed on the Mo-W alloys
of the varying compositions mentioned above to determine their
stress (dyn/cm.sup.2). The data indicate that since the stress is
markedly varied by the mixing ratio of Mo and W, the stress can be
decreased by adjusting the mixing ratio.
FIG. 4 shows the results of the test performed on Mo-W alloy film
obtained by sputtering Mo-W targets to determine their sputter
rates (nm/min). The sputter rates were determined by the following
method. First, the points selected on the lines drawn from the four
corners of a given glass substrate to the central part of the
substrate and the points selected on the lines drawn from the
central parts of the four sides of the substrate to the opposed
sides of the substrate were marked with an oily ink for the purpose
of degrading the adhesiveness of a Mo-W alloy film to be formed by
sputtering. Then, the Mo-W alloy film was formed by sputtering and
the portions of the Mo-W alloy film deposited on the portions
marked with the oily ink were peeled off the substrate by applying
an adhesive tape to the portions and peeling the adhesive tape from
the surface of the Mo-W alloy film. Thereafter, the oily ink was
exclusively wiped off with an organic solvent to expose the glass
substrate. The differences of level between the portions from which
the Mo-W film was peeled by the adhesive tape and the portions from
which no Mo-W film was peeled with the aid of a level difference
tester at fixed positions selected on the lines drawn from the edge
parts to the central parts. The film thicknesses thus found were
compared as sputter rates (nm/min).
It is clearly noted from FIG. 4 that the sputter rate improved in
proportion as the ratio of W tended to decrease. In consideration
of the resistance to etchants shown in FIG. 2, the data of FIG. 4
are believed to indicate that the proportion of W ought to be in
the range of from 25 to 45 at %.
The working example described above is one embodiment of this
invention. It can be modified with the thicknesses of the component
layers and the methods of film formation suitably altered.
Notwithstanding such modifications, this invention produces the
same effect as is obtained in the present example. The TFT may be
in some other structure such as is obtained by providing stoppers
for the insulating film on channels. The storage capacity part may
be in such a structure that it is formed in wirings in the same
layer as the gate electrode and in wirings in the same layer as the
data wirings.
EXAMPLE 2
Uniform mixed powders were obtained by weighing out a Mo powder
having an average particle diameter of 10 .mu.m and a W powder
having an average particle diameter of 10 .mu.m in amounts
calculated to account for varying atomic percentages of the
proportion of W in the range of from 20 to 95 at %, placing each
set of Mo and W powders in a ball mill having the inner wall
thereof coated with Mo, and mixing them for 30 hours by the use of
balls made of nylon. The mixed powders were each packed in a
shaping mold and shaped by a wet-CIP treatment under pressure of
200 MPa. The shaped masses consequently obtained were sintered in
an ambience of hydrogen under the conditions of 2073 K.times.10
hours to obtain sinters having density of 90%. The sinters thus
obtained were each subjected to the mechanical workings of cutting
and grinding to produce Mo-W targets measuring 250 mm in diameter
and 8 mm in thickness and having a varying composition. These Mo-W
targets were each bonded with an In type solder to a packing plate
made of oxygen-free copper and set in place in a sputtering
device.
FIG. 6 is a cross section of the arrangement of a TFT and a storage
capacity part used in a liquid crystal display device different
from the one used in Example 1. The construction and the process of
the TFT and the storage capacity part will be described below.
On a glass substrate 11, a prescribed wiring metal such as Mo-Ta
was sputtered in 300 nm to form simultaneously a gate electrode 12,
an address line, and a Cs line 19. Then, by the plasma CVD, a-Si
islands were formed by continuously depositing an oxide film or a
nitride film 13 in a thickness of 350 nm, an a-Si layer 14 in a
thickness of 300 nm, and n.sup.+ a-Si layers 5a and 5b each in a
thickness of 50 nm. Subsequently, a contact hole was formed by
etching with dilute hydrofluoric acid and the surface oxide film
was removed.
Then, by sputtering the Mo-W target of this invention mentioned
above and wet etching it, a source electrode 16a, a drain electrode
16b, and data wiring were simultaneously formed. An oxide film 17
was formed in a thickness of 300 nm and a contact hole was formed
on the drain electrode 16b by either etching with a HF type solvent
(at an etching rate of about 10 nm/min, for example) or dry etching
with such a gas as CF.sub.4 (at an etching rate in the rate of
about 3 to 10 nm/min, for example) and a picture element electrode
18 was formed in a thickness of 120 nm by sputtering ITO.
The Mo-W wiring thin film which was formed with the Mo-W target of
this invention mentioned above excelled in chemical resistance as
described in Example 1. The data wirings formed of the Mo-W wiring
thin film excelling in chemical resistance as described above could
be effectively subjected to a tapering work without entailing
deterioration of a resist by using an alkali etchant (pH
7.about.13) containing an oxidizing agent of high redox potential
instead of the etchant which would be used for etching a Mo film or
a W film.
In the picture element array consequently formed, since the data
wirings were given a tapering work, the interlayer insulating film
formed on the data wirings had fully satisfactory step coverage and
could retain dielectric strength at a high level. Further, since
the drain electrode 16b excelled in chemical resistance, a contact
hole could be formed by etching with hydrofluoric acid on the drain
electrode 16b and the picture element electrode could be worked
with a mixed liquid consisting of chlorine with nitric acid.
Moreover, the wirings formed with the Mo-W wiring thin film of the
present invention, unlike those formed with Al, were found to
generate no hillock and have no use for a barrier metal because
they were incapable of reacting with ITO.
As demonstrated in Example 1, the Mo-W wiring thin film of this
invention possesses basically low resistance and, because the
stress thereof is notably varied by the mixing ratio of Mo and W in
the Mo-W alloy, is allowed to lower the stress as required.
The working example described above is one embodiment of this
invention. It can be modified with the thicknesses of the component
layers and the methods of film formation suitably altered.
Notwithstanding such modifications, this invention produces the
same effect as is obtained in the present example. The TFT may be
in some other structure such as is obtained by providing stoppers
for the insulating film on channels. The storage capacity part may
be in such a structure that it is formed in wirings in the same
layer as the gate electrode and in wirings in the same layer as the
data wirings.
EXAMPLE 3
Uniform mixed powders were obtained by weighing out a Mo powder
having an average particle diameter of 10 .mu.m and a W powder
having an average particle diameter of 10 .mu.m in amounts
calculated to account for varying atomic percentages of the
proportion of W in the range of from 20 to 95 at %, placing each
set of Mo and W powders in a ball mill having the inner wall
thereof coated with Mo, and mixing them for 24 hours by the use of
balls made of nylon. The mixed powders were each packed in a
shaping mold and shaped by a wet-CIP treatment under pressure of
200 MPa. The shaped masses consequently obtained were sintered in
an ambience of hydrogen under the conditions of 2073 K and 8 hours
to obtain sinters having density of 90%. The sinters were each
subjected further an HIP treatment under the conditions of 2073 K,
4 hours, and 180 MPa to obtain sinters having density of 98%. Then,
the sinters thus obtained were subjected to the mechanical workings
of cutting and grinding to produce target pieces measuring 180 mm
in length, 180 mm in width, and 6 mm in width. The target pieces
were joined side by side in three columns and two rows to obtain
Mo-W targets. These Mo-W targets were each bonded with an In type
solder to a packing plate made of oxygen-free copper and set in
place in a sputtering device.
FIG. 7 is a cross section of the TFT and the storage capacity part
to be used in a liquid crystal display device different from the
ones used in Examples 1 and 2. In the liquid crystal display device
of this invention, like that of Example 1, the Mo-W target of this
invention mentioned above was sputtered in 300 nm to form a gate
electrode 22, an address line, and a Cs line 29a simultaneously on
a glass substrate 21. Then, in the same manner as in Example 2, the
Mo-W target of this invention was sputtered and subsequently wet
etched to form a source electrode 26a, a drain electrode 26b, and
data wirings simultaneously.
The liquid crystal display device of Example 3 uses a TFT so
constructed as to have stoppers for the insulating film provided on
channels instead of the TFT of the back channel cut type having the
channel part etched as adopted in Example 2. The storage capacity
part was formed with wirings laid in the same layer as the gate
electrode and ones laid in the same layer as the data wirings.
Specifically, the Mo-W target of this invention was sputtered to
form the gate electrode 22, the address line, and the Cs line 29a
simultaneously on the glass substrate 21. Then, an interlayer
insulating film 23, an a-Si layer 24, a channel protecting layer
30, and n.sup.+ a-Si layers 25a and 25b were formed sequentially.
Subsequently, by sputtering the Mo-W target, a source electrode
26a, a drain electrode 26b, data wirings, and a Cs line 29b were
simultaneously formed. Then, an oxide film 27 was formed and a
contact hole was formed on the drain electrode 26b, and a picture
element electrode 28 was formed.
According to Example 3 described above, the effect obtained in
Example 1 and that obtained in Example 2 were both obtained at the
same time.
This invention is not limited to the working examples described
above. The semiconductor is not limited to the a-Si but may be a
p-Si, a CdSe, or the like instead. The insulating film on the data
wirings is not limited to an oxide film but may be a nitride film.
Further, in the wiring thin film of this invention, two or more
superposed films formed of Mo-W alloys of different compositions
may be formed in the place of the one-layer films used in the
working examples. The wiring thin film of this invention may be
vested with improved resistance to oxidation by having a layer of
Ta, Tan, or the like superposed on the wiring thin film. The wiring
thin film of this invention may have the resistance thereof lowered
by having a layer of Al, Cu, or the like superposed on the lower
side of the wiring thin film.
EXAMPLE 4
Mixed powders prepared by mixing a Mo powder having an average
particle diameter of 4.5 .mu.m and a W powder having an average
particle diameter of 3.6 .mu.m at prescribed ratios were each
packed in a rubber shaping mold and subjected to CIP under pressure
of 200 MPa to produce shaped masses. The shaped masses were
sintered in an ambience of hydrogen under varying conditions, which
were as shown in Table 2 and Table 3. The resultant sinters were
heated in an ambience of hydrogen and hot rolled crosswise. The
rolling conditions were as shown in Table 2 and Table 3. The rolled
blanks consequently obtained were heat-treated under the conditions
shown in Table 2 and Table 3 and then mechanically worked to
produce Mo-W targets measuring 250 mm in diameter and 8 mm in
thickness. The Mo-W targets, No. 1 through No. 40, shown in Table 2
and Table 3 were thus obtained.
Referential Examples (No. 41 through No. 48) shown in Table 3 cover
Mo-W targets manufactured by following the procedure of Example 4
while setting any of the conditions for sintering in hydrogen, the
conditions for rolling, and the conditions for heat treatment
outside the preferred ranges specified by this invention.
TABLE 2
__________________________________________________________________________
Conditions Conditions for for sintering in Conditions for heat
Compo- hydrogen rolling treatment sition Temper- Temper- Rolling
Temper- Sample (at %) ature Time ature ratio ature Time No. W Mo
(K) (hr) (K) (%) (K) (hr)
__________________________________________________________________________
Example 4 1 25 bal 2173 15 1673 55 1773 3 2 25 bal 2173 25 1773 61
1873 3 3 25 bal 2273 25 1773 62 1873 3 4 25 bal 2473 10 1773 69
1673 3 5 25 bal 2473 24 1773 74 1773 3 6 30 bal 2173 20 1673 51
1673 3 7 30 bal 2273 30 1773 64 1673 3 8 30 bal 2373 25 1873 69
1773 3 9 35 bal 2173 20 1773 56 1773 3 10 35 bal 2373 25 1773 64
1773 3 11 35 bal 2473 15 1773 72 1673 3 12 35 bal 2473 24 1873 74
1873 3 13 40 bal 2273 15 1673 58 1873 3 14 40 bal 2473 10 1773 67
1673 3 15 40 bal 2473 24 1973 72 1773 3 16 45 bal 2373 25 1773 58
1673 3 17 45 bal 2373 10 1873 60 i673 3 18 45 bal 2473 24 1873 70
1773 3 19 50 bal 2173 15 1773 61 1773 3 20 50 bal 2273 25 1873 68
1873 3 21 50 bal 2373 24 1873 69 1673 3 22 50 bal 2373 30 1873 68
1773 3 23 50 bal 2473 18 1873 70 1673 3 24 60 bal 2273 20 1773 56
1773 3
__________________________________________________________________________
TABLE 3
__________________________________________________________________________
Conditions Conditions for for sintering in Conditions for heat
Compo- hydrogen rolling treatment sition Temper- Temper- Rolling
Temper- Sample (at %) ature Time ature ratio ature Time No. W Mo
(K) (hr) (K) (%) (K) (hr)
__________________________________________________________________________
Example 4 25 60 bal 2373 24 1973 69 1673 3 26 60 bal 2373 30 1773
66 1673 3 27 60 bal 2473 30 1973 66 1673 3 28 65 bal 2373 25 1873
60 1873 3 29 65 bal 2473 10 1973 54 1773 3 30 65 bal 2473 24 1973
73 1873 3 31 70 bal 2473 10 1773 70 1973 3 32 70 bal 2473 25 1773
68 1673 3 33 70 bal 2473 25 1873 72 1873 3 34 80 bal 2373 20 1773
62 1873 3 35 80 bal 2473 20 1873 64 1773 3 36 80 bal 2473 20 1873
70 1773 3 37 90 bal 2373 24 1873 59 1973 3 38 90 bal 2473 24 1973
60 1873 3 39 90 bal 2473 24 1973 75 1873 3 40 90 bal 2473 30 1873
71 1973 3 Refrential 41 30 bal 1973 24 1873 -- -- -- Example 42 30
bal 2073 8 1773 -- -- -- 43 40 bal 2073 25 1773 45 1773 3 44 40 bal
2373 25 1473 -- -- -- 45 40 bal 2373 25 1773 25 1773 3 46 40 bal
2473 25 -- -- 1673 3 47 40 bal 2473 25 1773 76 1073 3 48 40 bal
2473 25 1773 81 1673 3
__________________________________________________________________________
The Mo-W targets obtained in Example 4 and Referential Example
mentioned above were tested for relative density, average particle
diameter of grains, and Vickers hardness. The results were as shown
in Table 4 and Table 5. These Mo-W targets were each set in place
in a DC magnetron sputter device and sputtered on a 6-inch Si wafer
to form a Mo-W alloy film (in a thickness of 30 nm). The Mo-W alloy
films consequently obtained were visually examined to take count of
the numbers of particles of not less than 0.3 .mu.m existing in the
films. The numbers of particles thus determined by the visual
examination were those found in Mo-W alloy films which remained
after removal of edge portions 5 mm in width from the relevant
6-inch Si wafers. The results of this visual examination are
additionally shown in Table 4 and Table 5.
TABLE 4 ______________________________________ Average Relative
particle Vickers Number of Sample density diameter hardness
particles No. (%) (.mu.m) (Hv) (pieces)
______________________________________ Example 1 98.2 183 287 83 4
2 98.6 171 279 62 3 98.6 173 263 44 4 99.4 164 248 30 5 100 107 220
23 6 98.0 184 264 89 7 98.4 139 240 72 8 99.1 119 231 63 9 98.0 208
276 84 10 99.3 123 252 40 11 100 183 306 36 12 100 89 212 23 13
98.1 138 200 66 14 99.2 222 304 56 15 100 123 268 33 16 98.0 201
298 93 17 98.4 189 291 93 18 100 92 276 29 19 98.1 183 252 72 20
99.4 107 229 39 21 99.2 238 277 78 22 99.5 110 240 41 23 99.8 77
236 31 24 98.3 141 281 81
______________________________________
TABLE 5 ______________________________________ Average Relative
particle Vickers Number of Sample density diameter hardness
particles No. (%) (.mu.m) (Hv) (pieces)
______________________________________ Example 25 99.8 130 262 28 4
26 99.0 148 268 42 27 100 88 244 25 28 99.2 101 234 44 29 99.3 124
256 70 30 100 69 210 20 31 99.4 71 221 63 32 100 74 240 26 33 100
67 198 18 34 99.6 93 212 47 35 99.9 62 220 31 36 100 59 231 28 37
99.3 82 209 82 38 99.7 72 224 42 39 100 46 190 14 40 99.8 53 186 29
Referential 41 (breakage) -- -- -- Example 42 (breakage) -- -- --
43 97.3 183 292 186 44 (breakage) -- -- -- 45 93.8 89 261 312 46
90.4 46 171 387 47 100 206 373 138 48 100 326 296 122
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It is clearly noted from Table 4 and Table 5 that the Mo-W targets
obtained in Example 4 invariably had relative than 98% and Vickers
hardness, Hv, of not more than 350. It was further found that the
films formed of these Mo-W targets generated particles in markedly
lowered numbers.
An optical photomicrograph showing on a magnified scale (100
magnifications) the metallic texture of the Mo-W target, Sample No.
11, of Example 4 is given in FIG. 8, an optical photo-micrograph
showing on a magnified scale (100 magnifications) the metallic
texture of the Mo-W target, Sample No. 15 is given in FIG. 9, and
an optical photomicrograph showing on a magnified scale (100
magnifications) the metallic texture of the Mo-W target, Sample No.
31 is given in FIG. 10. Then, an optical photomicrograph showing on
a magnified scale (100 magnifications) the metallic texture of the
Mo-W target, Sample No. 47 of Referential Example is given in FIG.
11.
FIG. 8 shows the metallic texture in a state relieved of strain. In
contrast, FIG. 11 shows the metallic texture in a state not fully
relieved of strain because of a low temperature of the heat
treatment used for relief of strain. FIG. 9 and FIG. 10 show the
metallic textures both in a state relieved of strain and
recrystallized. The Mo-W targets of FIG. 9 and FIG. 10 were
thoroughly relieved of strain by being recrystallized. The Mo-W
targets particularly of this invention, therefore, prove ideal.
Though the metallic texture of FIG. 8 is in a state relieved of
strain, the degree of relief of strain is not so thorough as in the
metallic textures of FIG. 9 and FIG. 10. Thus, the Mo-W target of
FIG. 8 which retained strain to a certain extent had the
possibility of warping while in use and peeling off a backing
plate. It was in need of recrystallization. FIG. 10 shows a sign of
the occurrence of a few pores in crystals of the metallic texture
due to an unduly high temperature of the heat treatment performed
for the relief of strain. This fact indicates that the temperature
of the heat treatment ought to have been fixed at a level not so
high as to induce occurrence of such pores.
When the liquid crystal display devices shown in Example 1, Example
2, and Example 3 described above were manufactured with the Mo-W
target obtained in Example 4, they invariably showed fully
satisfactory results. Then, the Mo-W wiring thin film produced with
the Mo-W target of Example 4 generated particles in a markedly
decreased number and, hence, proved to be capable of further
enhancing the electrical properties of the address wirings and the
data wirings.
This invention is not limited to the constructions of the various
working examples cited above and the methods of production
described in these working examples. It can be embodied in all the
products using the Mo-W material and the Mo-W target according to
this invention and in all the products using the Mo-W wiring thin
film according to this invention. It is not limited to the wirings
and others of the liquid crystal display devices but may be
effectively used in wirings for plasma display devices, solid
display devices, and planar display devices using a field-emission
cold cathode.
Industrial Applicability
It is clearly demonstrated by the examples cited above that the
Mo-W material of this invention for the formation of wirings
manifests low resistance, permits a tapering work, and excels
tolerance for an etchant and, therefore, proves to be a highly
useful material for the formation of address wirings and data
wirings as in liquid crystal display devices. The Mo-W wiring thin
film of this invention uses the Mo-W material (Mo-W alloy) of the
quality mentioned above and, therefore, contributes immensely to
enhance the operating characteristics and the reliability of liquid
crystal display devices. The Mo-W target of this invention for the
formation of wirings allows the Mo-W wiring thin film of the
quality mentioned above to be formed advantageously with high
repeatability.
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